Vilfredo
Pareto

Vilfredo Pareto was a 19th century Italian economist, Vilfredo Pareto, who
noticed that around 80% of the wealth of the country was held by around
20% of the population (and that this was recursive: of the 20%, 80% of
their wealth was held by 20% of this privileged society, and so on).

Joseph Juran,
a 20th century quality consultant (and guru), noticed that this also
applied to defects, where around 80% of the problems would be in 20% of
the defects, which meant that if you focused on that 20%, you could have a
big effect with minimal effort. He called this the 'Pareto
Principle'.